1. Field of the Invention
The present invention relates to a micro-oscillator to be an element of a signal filter, mixer, resonator and the like, to a semiconductor device that includes the micro-oscillator, and to a communication apparatus in which a band-pass filter including the micro-oscillator is used.
2. Description of the Related Art
A micro-oscillator made by using the MEMS (Micro Electro Mechanical Systems) technology has been known. Since a micro-oscillator made by using semiconductor processes has such advantages as: an area occupied is small; a high Q value can be obtained; and integration with other semiconductor devices is possible, the micro-oscillator is proposed to be used as a high frequency filter within a radio communication device by the research institutes including the University of Michigan (refer to Non-patent Literature 1).
FIG. 1 shows a schematic view of a micro-oscillator, specifically a beam-type oscillator of electrostatic drive, constituting a high frequency filter described above. This oscillation element 1 includes: an input-side wiring layer 7 and an output electrode 4 which are, for example, made of polycrystalline silicon, formed on a semiconductor substrate 2 through an insulation film 3, and an electrode to be a oscillation plate, that is, a beam 6 formed to face the output electrode 4 separated by a space 5. The beam 6 straddles like a bridge to be connected to the input-side wiring layer 7 such that this beam is supported by anchor portions (support portions) 8 [8A, 8B] at the both ends. The beam 6 becomes an input electrode. An input terminal t1 is led out from the input-side wiring layer 7 and an output terminal t2 is led out from the output electrode 4. In this oscillator 1, a high frequency signal S1 is supplied through the input terminal t1 in a state in which a DC bias voltage V1 is applied between the beam 6 and the ground. When the DC bias voltage V1 and high frequency signal S1 are input to the input terminal 1, the beam 6 having a natural oscillation frequency determined by a length thereof oscillates by electrostatic power generated between the output electrode 4 and the beam 6. With this oscillation, a high frequency signal corresponding to temporal change of capacitance between the output electrode 4 and the beam 6 and the DC bias voltage is output from the output electrode 4 (therefore, from the output terminal t2 ). A signal corresponding to the natural oscillation frequency (natural frequency) of the beam 6 is output in a high frequency filter.
Non-patent Literature 1: C. T.-Nguyen, Micromechanical components for miniaturized low-power communications (invited plenary), proceedings, 1999 IEEE MTT-S International Microwave Symposium RF MEMS workshop, Jun. 18, 1999, pp 48-77.